In the manufacture of a liquid crystal display comprising thin film transistors (TFTs), for instance, thin film transistors are formed on a substrate through CVD or any other process. Since a fabrication process for forming thin film transistors on a substrate involves high-temperature treatment, a substrate made of a heat-resistant material is required, i.e., the substrate material must have a high softening point and a high melting point. At present, therefore, quartz glass is used as a material to provide a substrate capable of withstanding up to approx. 1000° C., or heat-resistant glass is used as a material to provide a substrate capable of withstanding up to approx. 500° C.
As mentioned above, the substrate on which thin film devices are to be mounted must satisfy conditions required for fabricating the thin film devices. Namely, the kind of substrate is determined to meet fabrication conditions required for the devices to be mounted thereon.
In view of a subsequent phase to be taken after thin film devices such as TFTs are formed, the substrate indicated above are not always preferable.
Where a fabrication process involving a high-temperature treatment is carried out, a quartz glass or heat-resistant glass substrate is used as exemplified above. However, the quartz glass or heat-resistant glass substrate is very expensive, resulting in an increase in product cost.
The glass substrate is also disadvantageous in that it is relatively heavy and fragile. A liquid crystal display for use in a portable electronic apparatus such as a palm-top computer or mobile telephone should be as inexpensive as possible, light in weight, resistant to deformation to a certain extent, and invulnerable to dropping. In actuality, however, the glass substrate is heavy, not resistant to deformation, and vulnerable to dropping.
In other words, there is a discrepancy between restrictive conditions required for a manufacturing process and characteristics desirable for a manufactured product. It has been extremely difficult to satisfy both of these required process conditions and desirable product characteristics.
The inventors, et al. have proposed a technique in which an object-of-transfer layer containing thin film devices is formed on a substrate through a conventional process and thereafter the object-of-transfer layer containing thin film devices is removed from the substrate for transference to a destination-of-transfer part (Japanese Patent Application No. 225643/1996). In this technique, a separation layer is formed between the substrate and a thin film device which is the object-of-transfer layer, and the separation layer is irradiated with light to cause exfoliation in an inner-layer part and/or interface of the separation layer. Thus, bonding strength between the substrate and the object-of-transfer layer is weakened to enable removal of the object-of-transfer layer from the substrate. In this manner, the object-of-transfer layer is transferred to the destination-of-transfer part. Where a fabrication process for forming thin film devices involves high-temperature treatment, a quartz glass or heat-resisting glass substrate is used. In the technique mentioned above, however, since the destination-of-transfer part is not exposed to high-temperature treatment, restrictive requirements imposed on the destination-of-transfer part are advantageously alleviated to a significant extent.
When the object-of-transfer layer containing thin film devices is removed from the substrate employed for thin film device formation so that the object-of-transfer layer is transferred to the destination-of-transfer part, the layering relationship of the object-of-transfer layer with respect to the destination-of-transfer part becomes opposite to that of the object-of-transfer layer with respect to the substrate. Namely, the side of the object-of-transfer layer which has faced the substrate originally does not face the destination-of-transfer part. For example, in the case where the object-of-transfer layer has first and second layers and is formed on the substrate in the order of the first and second layers, when the object-of-transfer layer is transferred to the destination-of-transfer part, the object-of-transfer layer is configured thereon in the order of the second and first sub-layers.
In the common practice of forming thin film devices on a substrate, electrodes are formed via an insulation layer after the formation of the element. Since the electrodes are disposed on the surface side, wiring connections or contacts can be arranged on the electrodes with ease. On the contrary, where the object-of-transfer layer containing thin film device and electrodes is transferred to the destination-of-transfer part, the electrodes are covered with the destination-of-transfer part, making it difficult to arrange wiring connections or contacts thereon.